<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      // 原型对象里面添加自定义方法
      Array.prototype.sum = function () {
        var sum = 0;
        for (var i = 0; i < this.length; i++) {
          sum += this[i];
        }
        return sum;
      };
      var arr = [1, 2, 3];
      console.log(arr.sum());
      var arr1 = new Array(1, 2, 3, 4);
      console.log(arr1.sum());
    </script>
  </body>
</html>
